1. Field of the Invention
The present invention relates to a DC power supply apparatus, in particular, a DC power supply apparatus for supplying a DC power to a plasma generating device for a sputtering.
2. Description of Related Art
According to an earlier development, in a process for producing a semiconductor or the like, as a power supply apparatus (hereinafter, occasionally referred to as xe2x80x9cDC power supplyxe2x80x9d) for supplying a stable DC power to a plasma generating device for a sputtering, a voltage type of DC power supply apparatus which functions as a voltage source for a load, was used.
FIG. 9 shows an example of a structure of a DC power supply 5 according to an earlier development. In FIG. 9, the DC source 5 comprises a breaker 3, a rectifier 11, a DC filter 12, an inverter 121, a transformer 14, a rectifier 15 and a DC filter 122.
The rectifier 11 is a bridge-type of three-phase full wave rectifying circuit or the like, which uses a diode or the like as a rectifying element. The rectifier 11 carries out a full-wave rectification of an AC power inputted from a commercial power supply unit 2 through the breaker 3, to convert it into a DC power.
The DC filter 12 is an LC filter having a DC reactor LF1 and a smoothing capacitor CF1, and smoothes the DC power rectified by the rectifier 11.
The inverter 121 comprises a bridge-connected semiconductor switch, and converts the DC power smoothed by the DC filter 12 into an AC power. The inverter 121 is a voltage type of inverter which is operated by a pulse width control, a pulse frequency control or the like.
The transformer 14 is one having two windings (a primary winding and a secondary winding) which are electromagnetically coupled with each other. The transformer 14 transforms the output voltage of the inverter 121, which is applied to the primary winding, according to the turn ratio thereof. Then, the voltage is generated by the secondary winding.
The rectifier 15 comprises a bridge-type of full wave rectifying circuit or the like, which uses a diode or the like. The rectifier 15 rectifies the AC power generated by the secondary winding of the transformer 14, to convert it into a DC power.
The DC filter 122 is an LC filter having a DC reactor LF3 and a smoothing capacitor CF3, and smoothes the DC power rectified by the rectifier 15.
As described above, after the DC power supply 5 generates a DC power by rectifying and smoothing the input AC power, the generated DC power is converted into an AC power by the inverter 121. After the voltage transformation, the DC power supply 5 outputs a DC power by rectifying and smoothing the AC power again. That is, the DC power supply 5 operates as a voltage source. The discharge current is determined in accordance with the output voltage and the impedance of the plasma generating device 4. That is, the DC power supply 5 is a voltage type of DC power supply apparatus.
During the plasma generation, if an arc discharge is caused in the plasma generating device 4, there is some possibility that a film is damaged. As a treatment for an arc discharge which is harmful to a film, the following three methods (I) to (III) have been used.
(I) A power supply is temporarily stopped.
In this case, when the generation of the arc discharge is detected, the operation of the DC power supply 5 is stopped. After a certain time elapsed, the operation thereof is restarted.
(II) A reverse voltage is applied by an LC resonance.
In this case, in the DC power supply 5, an LC resonance circuit having a reactance and a capacitor is provided between the DC filter 122 and the plasma generating device 4. By generating a reverse voltage by the LC resonance which is one of the resonance phenomena, the generated arc is self-arc-extinguished.
(III) A reverse voltage is applied by a semiconductor switch element.
In this case, in the DC power supply 5, a reverse voltage generating circuit 20 having a semiconductor switch element is provided between the DC filter 122 and the plasma generating device 4. When the generation of the arc discharge is detected, a reverse voltage is generated by the semiconductor switch element to forcedly arc-extinguish the generated arc.
Among the reverse voltage generating circuits, there are some ones which can detect the increase in discharge current or the decrease in discharge current and can forcedly arc-extinguish the arc before the arc current flows.
As described above, as a treatment for the arc discharge, there are three methods (I) to (III). According to the required quality of the film, one method was selected from the three methods (I) to (III).
However, the DC power supply 5 according to an earlier development, has the following problems.
(1) When the arc discharge is frequently generated, an output current cannot be controlled by the above methods (I) to (III).
In the method (I) in which the power supply is temporarily stopped, because the operation of the DC power supply 5 is stopped whenever the arc is generated, the operation of DC power supply 5 and the stop of the DC power supply 5 are frequently repeated. Further, in this method, because the energy of the DC filter 122 is released even though the operation of the DC power supply 5 is stopped, the film is damaged.
In the method (II) using the LC resonance or the method (III) using the semiconductor switch, while the arc-extinguishing operation is repeated, the output current of the DC power supply 5 gradually increases. When the output current exceeds a predetermined value, the DC supply source 5 is stopped by a protect circuit like the method (I).
In order to prevent the increase in output current, there was a method in which a DC reactor is inserted in series. However, because the DC reactor generally has a large size, the problems relating to the cost, the structure and the storage are occurred.
(2) The restart of the normal discharge is delayed.
In the method (I), because the DC power supply 5 is restarted, the time for restarting the DC power supply 5 is required. Even in the methods (II) and (III) in which the DC power supply 5 is not required to stop, the reflow of the discharge current which flows again is delayed by the wiring impedance and the like. Therefore, there is some possibility that the restart of the normal discharge is delayed.
In the present sputtering process, the discharge time tends to be shortened in one process. Therefore, when the arc discharge is frequently caused, the time delay caused by restarting the discharge is not negligible. As a result, the sum of time for the normal discharge becomes short. The degradation in quality of the film, such as a lack of thickness thereof is caused.
(3) Because the discharge current cannot be controlled for the constant voltage characteristic of the plasma generating device, the operation of the DC supply source 5 is not stable.
When the plasma generating device 4 treats as a load of the DC supply source 5, the voltage-current characteristics are close to the constant voltage characteristics. That is, although the current is largely changed on the basis of the intensity of the flowing DC power, the voltage is hardly changed. Therefore, for the DC supply source 5, the current is controlled more than the voltage by the control of the power to be supplied to the plasma generating device 4.
However, as described above, the DC power supply 5 is a voltage type of DC power supply apparatus which functions as a voltage source. That is, the DC power supply 5 supplies an output power as a voltage source. This easily causes the DC power supply to be unstable as compared with the DC power supply which function as a current source. Further, unnecessary resonance phenomena and the hunting are caused.
As described above, the DC power supply 5 according to an earlier development, has the above three problems (1) to (3). That is, the following three functions are required.
(a) An arc-extinguishment is certainly carried out and the output current is controlled even in the arc generating condition.
(b) After the arc discharge is extinguished, the normal discharge is immediately restarted.
(c) The discharge current is kept stable.
In order to solve the above-described problems, an object of the present invention is to realize a DC power supply which satisfies the above three requirements (a) to (c).
That is, in accordance with the first aspect of the present invention, a DC power supply apparatus for supplying a DC power to a plasma generating device, comprises:
an input section for converting an inputted AC power into a first DC power;
a current type of inverter connected with a next stage of the input section;
a transformer having a primary winding and a secondary winding, the primary winding being connected with the current type of inverter;
a rectifying section for rectifying a first AC power generated in the secondary winding of the transformer; and
a smoothing circuit for smoothing the rectified power which is rectified by the rectifying section;
wherein an electric energy to be supplied to the plasma generating device is controlled by controlling a switching operation of the current type of inverter as a current source.
According to the present invention, by controlling the switching operation of the current type of inverter, the electric energy to be supplied to the plasma generating device is controlled. That is, the so-called current type of DC power supply apparatus for supplying the stable DC power to the plasma generating device as a lord in a current source operation, can be realized.
In the plasma generating device as a load, the current is largely changed in accordance with the intensity of the inputted DC power. However, the plasma generating device has a property that the voltage is hardly changed. Therefore, by controlling the power not as a voltage source but as a current source, it is possible to control the power more stably.
Because the DC power supply is operated as a current source, the secondary current of the transformer does not be influenced by the impedance of the secondary circuit. Therefore, the DC reactor which must be provided on the secondary side of the transformer in case of the voltage source, is not required. The size of the apparatus can be minimized.
The current type of inverter may be a series-resonance type of inverter having a resonance reactor and a resonance capacitor which are connected in series.
The DC power supply apparatus further comprises a reverse voltage generating circuit which comprises:
a first tertiary winding which is electromagnetically coupled with the primary winding of the transformer;
a capacitor for rectifying a second AC power generated in the first tertiary winding and for storing a second DC power; and
a voltage applying section for monitoring whether an output voltage outputted to the plasma generating device is lower than a predetermined threshold value voltage, and for applying a reverse voltage to the plasma generating device by discharging the second DC power stored in the capacitor.
According to the present invention, a reverse voltage is applied to the plasma generating device. Therefore, when the arc is generated in the plasma generating device, it is possible to forcedly extinguish the arc immediately by applying the reverse voltage.
After the arc is extinguished, there is some possibility that the reflow of the discharge current is delayed by the property of the plasma generating device, the wiring impedance or the like. However, in this case, by discharging the energy stored in the DC reactor, the reflow of the discharge current is promoted to shorten the discharge suspending time after the arc extinguishment.
Depending on whether the output voltage is lower than the predetermined threshold value voltage, the reverse voltage can be applied. Therefore, because not the change of the output voltage (for example, the differential value) but the output voltage value itself is monitored, it is prevented that for example, the temporary voltage change which is caused by the restart of the normal discharge is judged to be the arc.
The DC power supply apparatus further comprises a power regenerative section which comprises a second tertiary winding which is electromagnetically coupled with the primary winding of the transformer;
wherein a third AC power generated in the second tertiary winding is rectified and is converted into a third DC power, the power regenerative section regenerates the third DC power to the input section.
According to the present invention, the transmitted power of the current type of inverter can be partially or wholly regenerated to the input section. For example, when the load of the plasma generating device is lightened and the power consumed by the plasma generating device is lower than the minimum power transmitted by the current type of inverter, the DC power supply apparatus cannot be controlled. In this case, by regenerating the power corresponding to the difference between the transmitted power of the current type of inverter and the consumed power of the load, to the input section, the stable control of the DC power supply apparatus can be realized in a broader output range.
The DC power supply apparatus further comprises a step-up section which comprises a third tertiary winding which is electromagnetically coupled with the primary winding of the transformer;
wherein by overlapping a fourth DC power obtained from a fourth AC power generated in the third tertiary winding and a main DC power obtained from the first AC power generated in the secondary winding of the transformer, the step-up section temporarily steps up an apparatus output voltage to be outputted from the DC power supply apparatus.
According to the present invention, the output voltage of the DC power supply apparatus can be temporarily stepped up. When the plasma generating device starts to operate, the high voltage which is required to start the discharge is supplied by temporarily increasing the output voltage. Therefore, the rapid and reliable discharge start can be realized. Further, when this function is used in only the case that the operation is started, the lord of the step-up section, which relates to the current, can be reduced.
The current type of inverter may comprise four semiconductor switches which are bridge-connected. Each semiconductor switch may be connected with a diode in anti-parallel.